There are numerous individuals who have become handicapped for some reason or another and are currently benefiting from the use of wheelchairs. Wheelchairs in general are well known art and have been around for sometime and therefore no detailed description need be given at this time. Many wheelchairs are lightweight and foldable to provide ease of transport. Such wheelchairs can be folded and can then fit into small spaces such as an automobile trunk. These wheelchairs have gained much popularity in recent years due to their lightweight and versatile properties. In order for the user of such a wheelchair to benefit they can either use their arms to push against the edges of the wheels or alternatively have someone push the rider to their desired location.
Unfortunately, many handicapped individuals using these wheelchairs desire to be independent of a second person pushing them around. These individuals need to have good strength in their arms in order to use these wheelchairs. This is especially true when attempting to climb hills.
In addition, the wheels tend to pick up debris and transfer it onto the hands of the user. Many wheelchairs employ a small steel ring just inside the wheel rim to allow the user to keep their hands relatively clean. This ring results in decreased torque due to the reduced available lever arm. It should be noted that some debris transfer may still occur.
It is often the case that an individual may not have sufficient upper body strength to use a hand powered wheelchair. In such instances an electric wheelchair is used. These wheelchairs are quite large and heavy and often weigh several hundred pounds. In addition, they tend to be complicated and expensive. If the battery dies or some part in the drive system breaks, the individual runs the risk of being stranded. Pushing an electric wheelchair with the arms can be a difficult if not impossible task to perform. This is especially true for individuals having reduced upper body strength.
The question of the weight of the electric equipment is critical to its usefulness for transportation of the wheelchair. Buses and subway trains are able to accommodate chairs and  bicycles that can be quickly driven into the opened door and equally driven out the same way and parked in the meanwhile inside the car with the minimum inconvenience to other travelers which we have adjusted to. This does not apply equally to the large and heavy electric wheelchairs which call for special ramps or cranes to be hauled with the vehicle and are themselves costly. This heavy equipment is taxing the strength of the disabled man and narrowing his choices. The extent to which public transportation can be an option to a handicapped person is critical to his or her mobility and is an intended part of this invention. The lightweight furthermore enables a person capable of driving an ordinary pickup truck or automobile to use it to transport the wheelchair without the need of heavy additional tooling. Hand in hand with the lightweight goes light cost and easy maintenance. The public sidewalk becomes a highway to a disabled man. The wheelchair that became mobile as an electric vehicle by adding a small electric scooter as described in this invention became at that same moment the most compact electric car for one person. In marrying the smallest two wheeled vehicle, the scooter, the boy's toy at the lowest cost. Here is an electric car in its ultimate simplicity, at its lowest cost, lightest weight, and least volume. The above is the essential part of this invention. Attach a scooter to a wheelchair. Make the scooter an electric scooter.
It is often the case that a handicapped person would need to travel significant distances but not want to be tied down by the difficulties arising from using traditional heavy electric wheelchairs. In addition it is desirable for such individuals to have the option of using their existing hand powered wheelchair with added electric power. In this way the existing wheelchair serves dual purposes and eliminates the need for having both an electric and a non electric wheelchair.
There are many systems available for adding electric power to lightweight human powered vehicles such as bicycles. These systems include the use of added electric motors and battery packs to bicycles to provide power assist to the rider. Many systems attach to the frame of the bicycle and have a motor that engages the tire by way of friction. Other systems engage the wheel by way of a chain. One particularly interesting system uses an added wheel that engages the ground to push the bicycle forward. This system is outlined in U.S. Pat. No. 6,290,014 invented by Paul MacCready, Jr. In his patent, MacCready describes a drive system that is suitable for driving a bicycle. This system is particularly interesting owing to the fact that  the drive wheel is independent of the other wheels. This independence or non-interference makes it particularly interesting for wheelchair propulsion applications.
Unfortunately, attempting to use any of these bicycle drive systems on wheelchairs has one major drawback. In order to convert an existing non electric push type wheelchair over to electric, suitable steering means needs to be added as well. When designing bicycle drive systems the issue of steering is not critical since the method of steering for an ordinary bicycle is the same as that of the electric bicycle. However when it comes to wheelchairs the story is significantly different. When a rider wants to steer a conventional wheelchair he or she changes the applied force on one wheel with respect to the other. This causes one side to travel faster than the other causing the wheelchair to change direction. In the case of a second person pushing the wheelchair, the pusher applies more force to one handle than the other. On the other hand, electric wheelchairs require steering mechanisms to make them work.
There is however a means capable of providing both propulsion and steering to an ordinary push type wheelchair. Two wheeled electric scooters have both steering and an independent drive wheel that engages the ground. Furthermore in many instances there is enough space between the drive and steering wheels for the wheelchair and rider to fit in between. Other scooters are low enough in profile and have small enough rear wheels to fit under the wheelchair without the rear wheel having to protrude out of the back end of the wheelchair. These scooters are available at low cost. When using an electric scooter to provide both steering and propulsion to a push type wheelchair all that is required is proper mounting means. Therefore the use of an electric scooter to convert an ordinary push type wheelchair over to electric becomes a relatively easy task to perform.
There are numerous electric scooters available. Some electric scooters may be more desirable than others. In general, the scooter needs to fit under the center of the wheelchair with the front end extending forward enough to provide useful and comfortable steering control. In addition, the scooter needs to be narrow enough to allow the front wheel of the wheelchair to swivel in their normal fashion without interference from the scooter.
The connection of the scooter and wheelchair needs to be such that the driving wheel rests against the ground with enough force to provide propulsion without excessive wheel  slippage. This becomes particularly important under the conditions of rough or bumpy terrain. Spring loading of the rear wheel is one option that may be used to modify traction on such terrain. In addition to providing good ground contact with the drive wheel, some positive suspension attributes may be realized as well.
It may also be desirable to spring load the front steering portion of the scooter to control traction with the ground. This approach may be used to improve steering control while still allowing the original wheels of the wheel chair to bear some of the weight.
Using the existing wheelchair wheels to bear weight may be desirable in certain instances. For example, many scooters have small wheels that can quickly wear out if used to bear excessive weight. This is especially true for many of the smaller scooters designed for use by lightweight individuals and children. These smaller scooters may be desirable to use if lightweight is important and if the required distance of travel is limited. Furthermore these smaller scooters often fit more easily under wheelchairs than their larger counterparts.
It may be desirable to allow for pushing of the modified wheelchair by the rider in the usual fashion of rotating the wheels by hand. Using the existing wheels of the wheelchair to bear a portion of the weight is one of the aspects of this invention allowing for use under a variety of varied conditions.
It may also be desirable to take advantage of the existing brake on an electric scooter or even to relocate the brake handle onto the back of the wheelchair to provide useful braking by a personal caregiver. For example, when a caregiver pushes a wheelchair, difficulties arise when going down hills. The person pushing the wheelchair has to hold back to keep the wheelchair from running away. Most push type wheelchairs have locking mechanisms on the wheels however these locking mechanisms are not suitable for braking when going downhill. Braking is commonly employed on scooters.
Alternatively, depending on the scooter design and geometry, it may be desirable to have the front steering wheel portion of the scooter bear all of the front end weight and thus lift the normal wheels in the front of the wheelchair completely off of the ground. Thus, depending on the desired result, a wide range of configurations is thus made possible based on particular needs. 
There are numerous electric scooters available in the marketplace. Some of these scooters are designed to be folded for ease of transport. Of particular interest is the no boundaries folding electric scooter. This particular scooter comes apart into two pieces with one of the pieces foldable for further compact storage and transportation. It should be noted that the front steering portion is powered and may be removed and attached directly to a conventional wheelchair thereby providing a simple conversion. This particular scooter has a relatively large seat and therefore has some resemblance to a wheelchair. Unfortunately, use of the arms by the rider for pushing the scooter forward is not a viable option and no provision is available for pushing the scooter by a second person such as a caregiver. With respect to these issues, this scooter while having good overall design features including modular construction is not as versatile as the converted electric wheelchair of this invention.
Many municipalities have local ordinances prohibiting the use of small wheeled vehicles such as scooters on sidewalks and other pedestrian locations. Many buildings do not allow scooters to enter. Wheelchairs however, are allowed in these areas and as such have more access than scooters. Converting an already existing wheelchair to electric allows the rider access to more places than would otherwise be available with a scooter.
The addition of an electric scooter to a conventional push type wheelchair provides a simple and low cost way of obtaining an electric powered wheelchair. The modular construction design features of this invention allow for an existing wheelchair to become electric powered by the incorporation of an off the shelf electric scooter. It may also be desirable to incorporate other features in a modular format as well. For example, range extension can easily be achieved by the addition of a lightweight battery pack or other source of electric power. Such sources include but are not limited to high energy density batteries such as nickel metal hydride, or lithium ion, fuel cells, solar panels, or even a small generator powered by a lightweight internal combustion engine.
Modular components provide a way to quickly and easily assemble the desired final electric powered wheelchair. In addition, modular components provide for ease of transport and reduce lifting requirements by reducing the weight of the heaviest components. 
In addition to scooters, it may be desirable to design a drive system and steering system that specifically fits standard push type wheelchairs. It may be desirable to have the steering portion connected to the drive portion as is the case with electric scooters or alternatively keep them as separate removable components for easier transport. It should be noted that either way, an easily transportable lightweight electric wheelchair is the result.